In an energy storage device, it is indeed a necessity to develop a flexible binder-free electrode. However, the rational design of such a binder-free electrode with high energy density and long cyclic stability is a great challenge for the scientific community. Herein, Se-anchored NiCoP nanoparticles have been developed that are in situ decorated on the surface of polyacrylonitrile-based heat-treated flexible carbon nanofibers (CNFs). The as-designed electrode demonstrates a remarkable specific capacitance/ capacity of 994 F g −1 /497 mAh g −1 at 1 A g −1 . The flexible solid-state symmetric supercapacitor (SSC) device delivers 76.86 Wh kg −1 energy density at a power density of 843.75 W kg −1 at 0.75 A g −1 and retains a promising energy density of 22.75 Wh kg −1 at an ultrahigh power density of 11250 W kg −1 at 10 A g −1 , respectively. The device also shows excellent long cyclic stability in terms of 94.12% capacitive retention along with 98.65% Coulombic efficiency after 15000 cycles at an applied high current density of 10 A g −1 . The synergetic effect of Se-anchored NiCoP with CNF along with the significant protection of NiCoP by a thin graphitic shell as well as suitable anchoring of electroactive materials on a CNF matrix via Se bridging may help to achieve such a high-performance energy storage device. The four sets of 1 × 1 cm 2 prototype devices (connected in series) are capable of enlightening a red-light-emitting diode (2.2 V) for 8 min and rotating a 3 V electric direct-current motor for 4 min via charging through a standard Si solar panel (6 V) illuminated by a 50 W street light for 2 min. The study creates an avenue toward the realistic drive of renewable energy conversion via the development of a high-performance flexible energy storage device.

Developing an efficient capacitive matrix along with the emergence of battery-type characteristics is the key priority function to attain high-performance asymmetric supercapacitors (ASCs). The rational design of metal-rich transition metal phosphides with a remarkable electrochemical activity and rich valence state possesses an efficient approach to overcome their limitation toward the low-rate capability with poor cycle life against metal deficient counterparts for their practical application. Herein, the metal-rich porous vanadium-doped nickel phosphide (V-Ni12P5) nanoflakes have been synthesized via a one-step solvothermal method. The as-synthesized electrode delivers a high specific capacity of 1455 F g–1 at a current density of 1 A g–1, and the corresponding assembled ASC device delivers a maximum energy density of 38.41 Wh kg–1 at a power density of 626.48 W kg–1 as well as long term cycling stability with 76.3% capacitive retention after 11,000 cycles. The assembled four sets of 1 × 1 cm2 devices in series designed with the help of a flexible carbon cloth matrix can light a red LED for 3 min and can rotate a 3 V home-designed windmill device for 1 min with in situ charging via a 6 V standard silicon solar panel illuminated by 50 W street light for 1 min. The flexible device can retain its invariant capacitive performance under rigorous twisting and bending at variable angles of 0, 90, and 135°. The significant enhancement (∼60%) of electrochemical activity for doped systems is mainly attributed to the generation of partial positive polarity on the metal centers and thereby induces strong adhesion of electrolytes under prolonged operation. Hence, this present work demonstrates the excellent capability of V-Ni12P5 nanoflakes toward the realistic drive of renewable energy conversion, unveiling the booming technology toward reliable high-performance hybrid energy-storage systems.

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Recently, metal oxide semiconductors, especially copper oxides, have engrossed researchers in the domain of solar cells due to their good optoelectronic properties. The present study reports the development of a heterojunction of CuO and Ta2O5 on pyramidal Si decorated with a thin MXene coating as a transparent conductive electrode. Further, the impact of annealing ambient on the crystalline quality and phase selectivity of the as-deposited Cu x O y film has also been investigated. The as-designed Si/Ta2O5/CuO/MXene heterostructure shows improved efficiency as compared to the counter device without a Ta2O5 passivation layer by 109 factors. The superiority of the as-designed heterojunction has been examined in terms of short-circuit current density of −10.5 mA/cm2 and photoconversion efficiency of ∼1.47%, respectively. Therefore, the work emphasizes the importance of the combination of n-Ta2O5 and p-CuO film as the wide- and low-band-gap materials for the future low-cost solar cell compatible with the Si process line technology.